It is common in drilling industries to use a drilling fluid, also called drilling mud, as a lubricant during drilling operations, such as drilling oil wells, drilling natural gas wells, and in exploration drilling rigs.
Drilling fluids perform various functions when implemented during a drilling operation. More specifically, drilling fluids can provide any of the following functions:                remove cuttings from the well        assist in the control of formation pressures        suspend and release cuttings        seal permeable formations        assist in maintaining wellbore stability        minimize formation damage        cool, lubricate and support the bit and drilling assembly        transmit hydraulic energy to downhole tools and bit        ensure adequate formation evaluation        control corrosion to acceptable levels        facilitate cementing and completion        minimize environmental impact        
During a drilling operation, there are a number of factors to consider when selecting the proper drilling fluid for a particular well. The cost, availability of specific products, and environmental impact are examples of factors taken into account when choosing a drilling fluid. The different properties that a drilling fluid will have are also taken into account when selecting a drilling fluid. The different properties of the drilling fluid can affect the desired functions of the drilling fluid. The affects on the desired functions must be realized and the drilling fluids must be designed according to their influence on all functions and relative importance for each function.
Drilling fluids can be provided with various additives, such as thinners, fluid loss control agents, corrosion inhibitors, weight materials, clays, and lost circulation materials, to develop drilling fluids having specific properties to target some of the specific functions listed above.
Generally, drilling fluids are pumped through a drill string, out of the drill string, and across the drill bit to clean and cool the drill bit. The drilling fluid then travels back up an annular space between the drill string and the sides of the hole being drilled in the formation. As the fluid travels up, the drilling fluid will eventually enter the annulus between the drill string and the surface casing and ultimately emerge at the surface. Once the drilling fluid has emerged from the surface, the cuttings can be removed and the drilling fluid can be stored and/or recycled back into the drill string.
A common problem in using drilling fluids is a phenomenon known as lost circulation. Lost circulation is a subterranean loss of the drilling fluid while drilling. Certain types of geological formations are porous and during drilling the drilling fluids have a tendency to migrate into the formation rather than traveling into the annulus between the drill string and the formation walls and eventually emerging at the surface. This loss of drilling fluid can become costly.
Lost circulation materials, such as ground cedar, pine fiber, ground walnut, peanut shells, shredded paper, ground mica, and calcium carbonate, have been added to drilling fluids to plug porous zones in the formation. This permits larger amounts of the drilling fluid to better travel up to the surface and be recovered. The use of these types of lost circulation materials adds significant costs to the drilling fluids, and thus the entire drilling operation. The increased costs are generated when the drilling fluid is recovered at the surface and processed to remove the drill cuttings from the recovered drilling fluid. When removing the drill cuttings from the drilling fluid, there is no way to differentiate between the drill cuttings and the lost circulation materials still contained in the drilling fluid. Thus, the lost circulation materials are removed along with the drill cuttings and have to be replaced with new lost circulation material. In the alternative, the drill cuttings and the lost circulation materials are left in the recovered drilling fluid and recycled back into the drill string. Over time, this causes a build up of the drill cuttings and the lost circulation materials in the drilling fluid and increases in the weight of the drilling fluid, which causes several negative effects on the well bore while drilling.